The acceptance of very clear evidence for the existence of the antisterility vitamin E has undoubtedly been delayed by certain discrepancies in dietary experiments. Different simplified and supposedly E free diets have yielded differing results as concerns their power to result in early and complete sterility in animals. We feel that we possess an adequate explanation of these discrepancies. Some investigators have reported widespread initial fertility with simplified diets, but their diets have frequently erred grossly by including fats now known to contain E—e. g., butter and Crisco. Some of them, however, contained no appreciable fat and yet fertility—at least initial fertility—resulted. We refer to the use of diets like our diet 223 (casein, 23; cornstarch, 73; salts, 4—daily separately 0.6 Gm. of yeast and 3 drops of cod liver oil) in which more than half of a group of animals are enabled to give birth to litters of living